The dynamics of electron self-exchange between nanoparticles.

The rate of electron self-exchange reactions between discretely charged metal-like cores of nanoparticles has been measured in multilayer films of nanoparticles by an electrochemical method. The nanoparticles are Au monolayer-protected clusters with mixed monolayers of hexanethiolate and mercaptoundecanoic acid ligands, linked to each other and to the Au electrode surface with carboxylate-metal ion-carboxylate bridges. Cyclic voltammetry of the nanoparticle films exhibits a series of well-defined peaks for the sequential, single-electron, double-layer charging of the 1.6-nm-diameter Au cores. The electron self-exchange is measured as a diffusion-like electron-hopping process, much as in previous studies of redox polymer films on electrodes. The average electron diffusion coefficient is DE = 10(+/-5) x 10(-8) cm2/s, with no discernible dependence on the state of charge of the nanoparticles or on whether the reaction increases or decreases the core charge. This diffusion constant corresponds to an average first-order rate constant kHOP of 2(+/-1) x 10(6) s(-1) and an average self-exchange rate constant, kEX, of 2(+/-1) x 10(8) M(-1) x s(-1), using a cubic lattice hopping model. This is a very large rate constant, considering the nominally lengthy linking bridge between the Au cores.

An ionic liquid form of DNA: redox-active molten salts of nucleic acids.

Ionic liquids are described that contain duplex DNA as the anion and polyether-decorated transition metal complexes based on M(MePEG-bpy)(3)(2+) as the cation (M = Fe, Co; MePEG-bpy = 4,4'-(CH(3)(OCH(2)CH(2))(7)OCO)(2)-2,2'-bipyridine). When the undiluted liquid DNA-or molten salt-is interrogated electrochemically by a microelectrode, the molten salts exhibit cyclic voltammograms due to the physical diffusion (D(PHYS)) of the polyether-transition metal complex. When M = Co(II), the cyclic voltammogram of the melt shows an oxidative wave due to the Co(III/II) couple at E(1/2) = 0.40 V (versus Ag/AgCl) and a D(PHYS) of 6 x 10(-12) cm(2)/s, which is significantly lower than that for Co(MePEG-bpy)(3)(ClO(4))(2) (D(PHYS) = 2.6 x 10(-10) cm(2)/s) due to greater viscosity provoked by the DNA polymer. When a 1:1 mixture is made of the Co(MePEG-bpy)(3).DNA and Fe(MePEG-bpy)(3)(ClO(4))(2) melts, two redox waves are observed. The first is due to the Co(III/II) couple, and the second is a catalytic wave due to oxidation of guanine in DNA by electrogenerated Fe(III) in the undiluted melt. Independent experiments show that the Fe(III) form of the complex selectively oxidizes guanine in duplex DNA. These DNA molten salts constitute a new class of materials whose properties can be controlled by nucleic acid sequence and that can be interrogated in undiluted form on microelectrode arrays.

Staphylococcus aureus cell extract transcription-translation assay: firefly luciferase reporter system for evaluating protein translation inhibitors.

The promoter for the Staphylococcus aureus capsule polysaccharide synthesis gene (cap1A) was cloned in front of the firefly luciferase gene for use in a cell extract S. aureus transcription-translation system. The assay is rapid, reproducible, and sensitive and has a lower background level than the radiolabeled amino acid incorporation translation assays. We present data evaluating a transcription inhibitor and a number of protein translation inhibitors in this system.

Redox and double-layer charging of phenothiazine functionalized monolayer-protected clusters.

Monolayer-protected Au clusters (MPCs) have been prepared with mixed monolayers of alkanethiolates and alkanethiolates terminally omega-functionalized with phenothiazine. The mixed monolayer MPCs can contain as many as 10 phenothiazines/MPC; these electron donors are electroactive in rapid, successive one-electron reactions. Surface adsorption of the functionalized MPCs is evident in cyclic voltammetry. Double-potential-step chronocoulometry with incremented potential steps was applied to unfunctionalized hexanethiolate-coated MPCs and to those functionalized with phenothiazine to analyze the coupling between the diffusion-controlled double-layer charging of the MPC cores and the oxidation of the phenothiazine centers. Apparent changes in ordering of the MPC alkanethiolate chains were observed with infrared spectroscopy in solutions of MPCs where alcohol, carboxylic acid, or phenothiazine moieties had been incorporated into the monolayer.

Enantioselective formation of arene oxides by direct oxidation of the arene.

Polycyclic aromatic compounds may be metabolized in humans to materials which are carcinogenic. These metabolites frequently contain an arene oxide group which is implicated in binding the metabolite to important biological substrates such as DNA. These enzymatic processes produce arene oxides in a highly enantioselective fashion. Direct oxidation of arenes by typical oxidants gives racemic oxide. We have been interested in converting arenes to arene oxides by direct oxidation in an enantioselective reaction. Three oxidation systems have been used to convert a variety of polycyclic aromatic compounds to arene oxides in processes which gives modest enantiomeric excesses.

Monolayer-protected cluster molecules.

In this report, we evaluate the present state of the rapidly emerging field of monolayer-protected cluster (MPC) molecules with regard to their synthesis and monolayer functionalization, their core and monolayer structure, their composition, and their properties. Finally, we canvass some of the important remaining research opportunities involving MPCs.

Orthopedic patients' satisfaction with their health care plan: a study performed by the Research and Education Committee of the Texas Orthopaedic Association.

To determine the satisfaction of orthopedic patients in regards to their health care plan, a four-page questionnaire was designed, pilot tested, and sent to 200 orthopedic surgeons randomly selected from members of the American Academy of Orthopaedic Surgeons in Texas. Fifty-seven orthopedic surgeons were not eligible to participate; our eligible cohort was 143 orthopedic surgeons. These surgeons were asked to administer the questionnaire to 20 randomly selected patients. Fifty-six of the 143 orthopedic surgeons participated, and surveys were completed by 939 patients. Patients were asked to rate their satisfaction with their health insurance, access to primary care physicians, and access to orthopedic surgeons. Although satisfaction was generally high, the patients with a gate-keeper (no direct access to specialists) were significantly less satisfied with their access to primary care physicians and orthopedic surgeons than those without a gatekeeper.

Arene dioxides of substituted pyrenes: synthesis and X-ray structural studies.

The arene dioxides of five 1-substituted pyrenes have been synthesized using dimethyldioxirane. The diasteroisomeric distribution of the dioxides has been determined. X-ray crystallographic structures of the dioxides have also been obtained. These structures show that for the cis dioxides the molecular structures show a departure from planarity, the extent of which is dependent on the substituent.